1. Field of the Invention
The present invention relates to a liquid repellent member, a method for manufacturing such a liquid repellent member, an ink jet head using such a liquid repellent member, a method for manufacturing such an ink jet head, and a method for supplying ink.
2. Description of the Related Art
In the past, a liquid repellent member having a surface for increasing a contact angle with respect to liquid has been used as various applications for various purposes. For example, the liquid repellent member is used in an ink jet head. In some ink jet heads, a discharge port constituting member for defining a plurality of discharge ports for discharging ink has a discharge port surface in which the plurality of discharge ports are formed, and such a discharge port surface is constituted by a liquid repellent member having liquid repellency.
Conventionally, as disclosed in U.S. Pat. Nos. 4,694,308, 4,716,423, 5,262,802 and 5,300,959, the discharge port constituting member of the ink jet head has been formed from nickel, polysulfone resin or polyimide resin. Further, in some examples, such a member is formed from a metal plate such as stainless steel, rather than nickel.
In order to achieve the liquid repellency of the discharge port surface of the discharge port constituting member, for example, when the discharge port constituting member is formed from polysulfone resin or polyimide resin, the repellency is realized by coating fluoride on the discharge port surface or by performing fluorine-plasma treatment. However, when the fluoride is coated, the fluoride is easily peeled by stress in a wiping operation, and, when the fluorine-plasma treatment is used, since the fluoride is merely formed as a surface layer of the discharge port surface having a thickness of about several Å, the fluoride is lost by wear due to stress in the wiping operation or the entire surface of the discharge port surface is not covered by the fluoride to create a surface portion having no fluoride, with the result that adequate liquid repellency cannot be obtained.
For example, Japanese Patent Application Laid-Open No. 05-116325 (1993) discloses a method (fluorine-plasma treatment) for forming a liquid repellent film having F—C bonding by forming a carbon skin film by deposition and by effecting discharging of the carbon skin film under the presence of nitrogen fluoride compound to generate plasma including fluorine.
According to this method, it is merely taught that a condition of the liquid repellent film has F—C bonding. Further, a liquid repellent level of the liquid repellent film is evaluated to be similar to a liquid repellent level obtained when the fluorine-plasma treatment is effected with respect to carbon included in organic resin itself such as polysulfone. This means that the entire surface of the liquid repellent film is not always in the F—C bonding condition.
Now, the reason will be explained.
When a carbon film is formed on a substrate 21 as shown in FIG. 25A by deposition, gloss of a surface of the substrate 21 is being lost. The reason is that, when fine carbon particles 22 are adhered to a film forming surface under the vacuum, since deposit as shown in FIG. 25B is formed, the surface becomes unevenness microscopically.
Thus, although it looks like that an F—C film is formed through the entire surface, as shown in FIG. 25C, microscopically, since the fluorine-plasma is not adhered to bottoms 24 of recesses and shadow areas of the fine carbon particles 22, the F—C film 23 is hard to be formed through the entire surface, and, in many cases, the entire F—C film is not formed.
Thus, by the method for effecting the fluorine-plasma treatment with respect to the carbon deposit film, an ink repellent film having ink repellency similar to that in the method for for effecting the fluorine-plasma treatment with respect to the polysulfone resin is merely obtained. That is to say, in the obtained article, areas 24 having no ink repellent film are dotted on the discharge port surface (FIG. 26).
When clean ink (composition: PEG=15%; IPA=3%, water=82%) is discharged, it was found that the surface of the substrate having the ink repellent film formed in this way ensures adequate ink repellency even when wiping operations are repeated by 2000 times, but, when the wiping operations repeated by 3000 times, the ink repellency of the surface is reduced to decrease a contact angle to about 70°. In such a contact angle, good ink discharging cannot be achieved, thereby causing deviation and/or image unevenness.
Further, when an orifice plate is formed from stainless steel or nickel, water repelling particles such as fine Teflon particles are included by about 7% to 18% by plating or seizure to obtain the liquid repellency of the discharge port surface. However, since the size of the particle is greater than 0.01 μm and the particles are not dispersed uniformly, in some cases, the discharging direction may become unstable. In this way, in the conventional orifice plates, adequate liquid repellency and endurance of liquid repellency cannot be obtained.
Further, coefficient of thermal expansion of metal used as material of the orifice plate is about 12 to 20×10−6, and coefficient of thermal expansion of resin is about 8 to 200×10−6. However, regarding the resins having the coefficient of thermal expansion of about 8 to 12×10−6, in almost all cases, anisotropy is given by drawing/extending treatment so that the resin represents coefficient of thermal expansion of 8 to 12×10−6 in a lateral direction (certain given direction) and coefficient of thermal expansion of about 50 to 100×10−6 in a longitudinal direction (direction perpendicular to the certain given direction). Alternatively, a large amount of lithium oxide or ceramic filler representing negative coefficient of thermal expansion may be added to the resin.
In a case where the orifice plate is formed from a plate made of resin including such mix filler, when the discharge ports are formed in the orifice plate, shapes of the discharge ports will be distorted. In this case, when a diameter of the discharge port is about 60 μm, since the mix filler affects little influence upon the shapes of the discharge ports, the ink is discharged without any problem, but, when the diameter of the discharge port is smaller than about 15 μm, since the mix filler affects great influence upon the shapes of the discharge ports, the shapes of the discharge ports are greatly deformed, with the result that a stable image can almost not be obtained.
On the other hand, a plurality of recording elements provided in correspondence to the plurality of discharge ports to apply energy for discharging the ink to the ink are constituted by heat generating elements or piezo-vibration elements, and these elements are provided on a substrate made of silicon or ceramic. Coefficient of thermal expansion of the substrate is about 3 to 6×10−6/° C. Since such an ink jet head is driven to perform discharging operations by about 10000 times per second, a temperature of the head reaches about 70 to 80° C.
In such a condition, when a length of the ink jet head exceeds 0.85 inch (about 20 mm), the following problems will arise.
In a case where difference in coefficient of thermal expansion is greater than 4×10−6, if difference in temperature becomes about 60° C. (for example, the temperature of the head is changed from 20° C. to 80° C.), a relative position between the driving element and the discharge port will be changed by 4 μm or more.
If the difference is 4 μm, when the ink is discharged onto the entire surface of a recording medium by serial print, positional deviation of 4 μm is generated in every scan, thereby causing density unevenness.
Accordingly, in an ink jet head in which a length of the ink jet discharging element substrate is selected to 20 mm or more in consideration of the influence of the difference in coefficient of thermal expansion between the ink jet discharging element substrate and the orifice plate, the temperature of the head is detected, and, when the temperature change reaches 30 to 40° C., the driving of the head is temporarily stopped, and, after the head temperature is decreased, the print is re-started. Particularly, when photo-like image print is effected, further careful head driving is required.
In this way, when a length of discharge port array is increased or arranging density of the discharge ports is increased in order to achieve higher speed and highly fine recording, the positional relationship between the orifice plate and the discharge element substrate is deviated due to the difference in coefficient of thermal expansion, abnormal ink flying may be generated in the vicinity by both ends of the discharge elements or the head may be damaged.
As mentioned above, the characteristics required for the discharge port constituting member (orifice plate) are that the discharge port surface has high ink repellency and the endurance of the ink repellency is excellent and that the coefficient of thermal expansion of the substrate (discharge element substrate) on which the discharge elements are provided is substantially the same as that of the orifice plate. However, as mentioned above, the conventional discharge port constituting members cannot satisfy these characteristics.